1973 Volume 46 Issue 9 Pages 2646-2650
Rates of gas phase thermal hydrogen exchange and hydrogenolytic demethylation of toluene-2-d1, -3-d1, and -4-d1 are evaluated using flow apparatus at temperatures 675–750 °C in the presence of a large excess molecular hydrogen. Both the exchange and the demethylation obey three-halves order rate law indicating the chain mechanism carried by hydrogen atom, the former being found slightly faster than the latter. Rate parameters of the two reactions taking place concurrently are then correlated with the extended Hückel superdelocalizability values appropriate to methylcyclohexadienyl transient formation. Overall applicability of the dynamic index as a measure of reactivity of deuteriotoluenes toward hydrogen atom attack is taken as an additional support for the generally accepted chain mechanism whose rate-determining step consists of electroneutral hydrogen atom addition to aromatic nucleus.
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